Conventional electrophotographic printers have been provided with a fixing device for fixing toner images to paper. The fixing device includes a heating roller arranged with its axis extending in the width direction of the conveyed sheets of paper, and a temperature sensor such as a thermistor for detecting the surface temperature of the heating roller in order that the printer can control the fixing temperature.
A conventional fixing device has a non-contact thermistor disposed on a frame of the fixing device via a heat-insulating member. The non-contact thermistor measures the temperature of the heating roller in a region through which the paper passes in order to accurately control the temperature of the heating roller.